[Gdal-dev] JP2MrSID internal overviews problem

[Frank Warmerdam]

On 10/17/05, Sheykhet, Rostic <rsheykhet at sanz.com> wrote:
> Hi all,
>
> I am trying to access JPEG 2000 internal overview data. gdal_info
> reports that there are 12 overviews in the file.  When I try
>
> band = parentBand->GetOverview(nOverview);
...
> // CPLGetLastErrorMsg() =
> //"MrSIDRasterBand::IRasterIO(): Failed to load image. invalid or empty
> scene speficied [50013]"


Rostic,

Yikes!  It seems that IRasterIO's on the explicit overviews using
the MrSID SDK was completely broken.  I think I likely broke it
circa Sept 15th but I'm not at all sure of that.

In any event, I have committed a fix and also added a test to the
"mrsid" gdalautotest script so such problems will come to light more
quickly in the future.  You can grab the fixed mrsiddataset.cpp at:

  http://www.gdal.org/srctree/frmts/mrsid/mrsiddataset.cpp

> I've looked at the code and it looks like it attempts to determine the
> best overview to use
> whithin the  RasterIO() call.  What are the rules for specifying
> overviews explicitly vs. letting the GDAL handle them?

Normally you can just do a RasterIO() request on the full resolution
layer and GDAL will use the most appropriate overview level as needed.
This aspect should have been working fine and is the normal case.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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